The present invention relates to vehicular-mounted apparatus for filling cracks in roadways and more particularly to an improved crack sealant apparatus and method for its use.
Asphalt generally is defined as the residual material obtained from the distillation of asphalt-based petroleum. Crude asphalt-based petroleums may be divided into three broad categories: asphaltic petroleums which may contain as high as 70% asphaltic bodies and generally high in solid paraffins; semi-asphaltic petroleums containing moderate amounts of asphaltic bodies which will not be generated during the distillation process; and non-asphaltic petroleums which do not carry asphaltic bodies but may generate them during distillation. Chemically, asphalts are complex aggregations of rather large aliphatic and cyclic hydrocarbon molecules. Besides the obvious hydrocarbon content, additional constituents in asphalts may include oxygen, sulfur, and nitrogen, often in substantial quantities, and iron, nickel, and vanadium present usually in trace quantities. For analytical purposes, asphalts commonly are split into two categories: asphaltenes and petrolenes. Asphaltenes are hard, friable materials insoluble in pentane. Asphaltenes are composed of hard resins and carbenes which are saturated hydrocarbons insoluble in pentane. Asphaltenes impart hardness and high softening temperature to the asphaltic compositions. Asphalts low in asphaltenes commonly are brought up to specification by catalytic oxidation and are referred to as "blown asphalts". Petrolenes are soluble in n-pentane and are composed primarily of viscous resins which can be isolated by other solvent combinations or by adsorption on surface-active clays. Petrolenes tend to impart ductility to the asphalt.
Asphaltic mixtures composed of mineral aggregate and bituminous constitutents are widely used in the road construction industry. Four major types of asphaltic mixtures are used in highway construction and maintenance: hot mixes; cut-backs; anionic emulsions; and cationic emulsions. Hot mix asphalts are used extensively in main highway construction where greater durability is required. These asphalts are characterized by a high asphaltene content making them very hard and resistant to chemical decomposition. Typical penetration values for these asphalts are in the 40 to 80 range.
Cut-back asphalts are formed by the use of an inexpensive petroleum solvent which along with the asphalt is mixed with the aggregate. The solvent evaporates leaving the asphalt binder in use. Generally, light petroleum oils or napthas are used as solvents. Of course, environmental considerations militate against the use of cut-back asphalts due to the necessary solvent expulsion from these applied asphaltic compositions.
The two final forms of asphalt include anionic emulsions and cationic emulsions. As their name implies, such emulsions are formed by the use of anionic or cationic emulsifiers for forming an oil-in-water emulsion which can be combined with aggregate for use in the road construction industry.
Aggregate used in road construction can be hydrophilic or hydrophobic depending upon the nature of the material. While the aggregate can include various mineral materials such as cinders or slags, typically the aggregate is of natural origin, such as sand, rock, or the like, typically native to the localities where the roads are being built. For example, limestone, dolemite, silica, sedimentary, metamorphic, or igneous rocks of various other kinds regularly are used in road building. Such mineral aggregates are hydrophilic in character, which characteristic generally has been considered to be primarily responsible for the existence of bitumin stripping. Stripping is defined as the breaking of the adhesive bond between the aggregate surface and the asphaltic material. When this bond is broken, the pavement is weakened and various forms of pavement distress, such as cracking or surface raveling, result.
Just as the presence of moisture inhibits a good asphalt-aggregate bond from being formed which contributes to asphalt stripping difficulties, moisture which finds its way into the interior of the roadway can contribute to pavement distress. Especially in climates subject to freezing and thawing, especially during winter months, moisture which penetrates to the interior of the pavement can be quite damaging. The volumetric expansion of water freezing causes cracks to develop which leads to premature deterioration of the roadway. Highway maintenance departments are called on to remedy premature pavement distress, yet are faced with necessary monetary and manpower constraints with respect to maintenance of such distressed roadways. Since constant capping is not economically feasible, highway maintenance departments have turned to the use of crack sealants for extending the longevity of the pavement. It is not unusual to see roadway crews effecting such cracked sealing operations in locales ranging from city streets to country roads. State and local specifications typically require the maintenance crew to utilize high pressure air to clean the crack from loose debris as well a clean the adjacent area around the crack on the roadway surface. Thereafter, a hot, asphaltic material is applied down in the crack as well as to the immediate adjacent roadway surface around the crack. Asphaltic materials utilized in crack sealing operations often are reinforced with polypropylene or another polymeric fiber. The reinforcing fiber provides a strain absorbing interlayer to prevent water penetration and provide firm adherence to the existing pavement.
Present-day apparatus for applying reinforced asphaltic crack sealants typically utilize a jacketed vessel for indirectly-heating the asphaltic crack sealant. Fuel oil or another heating media typically is disposed in the lower reservoir and is heated by propane or another fuel which can be safely transported and used. The interior of the vessel typically contains an auger mixing system for ensuring the homogeneous nature of the crack sealant, especially in view of the low density of the polypropylene or other polymeric reinforcing fiber. Unfortunately, hot spots within the oil bath typically develop along with necessary cold spots. If the asphaltic composition is heated too high (e.g. to a temperature of above about 350.degree. F. depending upon the type of fiber used), degradation of the reinforcing fiber can occur. Thus, temperature control is of prime importance, especially considering that minimum application temperatures typically range from about 275.degree. to 350.degree. F. By the time that the asphaltic composition reaches application temperature and the heating of the oil bath is discontinued, convective and like forces within the oil bath continue to distribute the heat from the area immediately adjacent the heating source to the remainder of the bath. This typically results in an overheating of the asphaltic crack sealant material housed within the vessel.